(1) Field of the Invention
The present invention relates to the improvement of a process for removal of hydrogen sulfide. More specifically, it relates to a process for removal of hydrogen sulfide which comprises a combination of an aqueous iron salt solution treatment and an electrochemical regeneration to recover sulfur and a hydrogen gas from a hydrogen sulfide-containing gas and which can inhibit the generation of industrial wastes (e.g., a waste iron solution, waste acids and waste iron salts), permits a long-term continuous operation in a closed system, and can efficiently recover sulfur and hydrogen.
(2) Description of the Related Art
Heretofore, hydrogen sulfide discharged in the refining of petroleum has been industrially treated by a Claus method. However, according to this method, a sulfur component in hydrogen sulfide can be recovered as sulfur, but a hydrogen component is converted into water without being recovered, and so the industrially efficient utilization of a hydrogen component cannot be realized.
Recently, as process for recovering sulfur and the hydrogen gas from hydrogen sulfide by means of oxidation and an electrochemical treatment, there are known methods in which an aqueous iron salt solution containing ferric ions is used. In such methods, various kinds of aqueous iron salt solutions containing the ferric ions are used, but in any process, the secondary production of a trace amount of sulfuric acid cannot be avoided. In consequence, sulfuric acid is accumulated in the aqueous iron salt solution, and the iron salt finally precipitates, which is a serious defect from the viewpoint of process.
As an improvement technique capable of eliminating this drawback, the group of the present inventors has already developed a technique in which an aqueous phosphoric acid-iron chloride solution is used to decrease the amount of secondarily produced sulfuric acid. However, subsequent researches have elucidated that the concentration of sulfuric acid in the aqueous iron-containing solution increases, while the solution is circularly used for a long time, and so it is necessary to blow down the aqueous iron salt containing solution as a waste solution in a certain ratio and to simultaneously make up the fresh aqueous iron salt containing solution in order to keep the suitable sulfuric acid concentration.